The invention firstly relates to bitumen (asphalt) or asphalt (asphalt cement) for the production of road surfaces.
Road surfaces are very widely produced in the form of asphalt or a mixture of bitumen with aggregates, such as sand, gravel, grit (round or crushed) or the like.
One aim in a road surface is to achieve high wear resistance. Furthermore, the deformation tendency should be low in order that unevenness, such as wheel tracks or the like, if possible does not occur, is slight or only occurs after a long period of use.
The invention is concerned with the technical problem of providing an improved bitumen or asphalt, in particular for the production of road surfaces.
This technical problem is firstly and substantially resolved wherein the bitumen or asphalt contains a proportion of paraffin obtained by a Fischer-Tropsch synthesis (FT paraffin) FT paraffins principally consist only of normal paraffins. More than 90% are usually n-alkanes. The remainder consists of iso-alkanes. The chain length is from C30 to about C100, with a gradation (solidification point, SP) from about 68 to about 105xc2x0 C. The proportion of FT paraffin is preferably 0.5% or more, based on a bitumen content of the asphalt or based on bitumen as such. In practice, these percentages are based on the weight. However, they can also be per cent by volume. Surprisingly it has been found that a road surface produced using bitumen or asphalt modified in this way is significantly more durable. The formation of wheel tracks under the usual loads occurring in road traffic due to motor vehicles is significantly reduced compared with conventional road surfaces based on bitumen or asphalt. The strength of a road surface is dependent on various interdependent factors, in particular, inter alia, on the degree of compaction. Surprisingly, it has been found here that the addition of FT paraffin facilitates significantly greater compaction. Although the FT paraffins ultimately result in a harder form of the road surface, in the liquid state they simultaneously reduce the viscosity of the xe2x80x9cbinding materialxe2x80x9d, i.e. the bitumen. They act as it were as xe2x80x9cfluidizersxe2x80x9d. The grit used, round or crushed, is also of importance with respect to the strength of the road surface. In the case of crushed grit, high strengths can be achieved, attributable to the intermeshing of the individual grit particles. However, better compaction can be achieved in the case of uncrushed, round grit or gravel. In this connection too, the addition of FT paraffins has advantageous effects. The adherence of bitumen to the stone, such as precisely this grit or gravel, is improved. A particularly significant improvement can be achieved ifxe2x80x94at least partiallyxe2x80x94oxidized FT paraffins are employed. Although this causes the solidification point to drop by about 5xc2x0 compared with non-oxidized FT paraffins, the abovementioned adherence is significantly improved, enabling the use of round gravel or grit, at least to a certain proportion, without reductions in strength having to be accepted. The advantageous effect of oxidized FT paraffins is attributed to the functional groups (polarity) which they thereby provide.
In practice, the proportion of FT paraffins is in the range from 0.5 to 10 per cent by weight, preferably in the range from 2.5 to 7.5 per cent by weight, and further preferably about 4 to 5 per cent by weight, based on the bitumen. Regarding the FT paraffins, a preferred range of use is those having a solidification point from 90 to about 105xc2x0 C.
Whereas standard asphalt, in the form of rolling asphalt, contains about 3 to 8% of bitumen, so-called mastic asphalt, which contains about 6.5 to 8.5% of bitumen, is also prepared. Bitumen grades of B45 or higher are usually employed here. In order to prevent settling of the mineral constituents during transport of mastic asphalt, it is necessary to effect constant stirring until final processing. In order to keep the viscosity low for this stirring, the mastic asphalt is kept at a relatively high temperature, namely at 200 to 250xc2x0 C. Surprisingly, the addition of FT paraffins, as explained above, in an approximately equal ratio to the mastic asphalt (or the bitumen of the mastic asphalt) results in it being possible significantly to lower the temperature which is necessary to keep the mixture stirrable. Whereas temperatures of at least 220 to 250xc2x0 C. were hitherto necessary, a reduction of 30xc2x0 C. is possible on addition of FT paraffins. This lowering in the temperatures is at the same time accompanied by the considerable advantage that release of harmful substances is reduced.
In asphalt, such as mastic asphalt or even rolling asphalt, it has also been found that a significantly longer time is available for working or processing the asphalt. Surprisingly, it has been found that the processing of this asphalt was also possible at lower temperatures than hitherto. Besides the reduction in viscosity described above, this effect is also attributed to a latent heat storage effect of the paraffin. On phase conversion of the paraffin, heat liberation takes place without a reduction in temperature.
Furthermore, the invention also relates to a road surface consisting of a lower layer of sand/gravel (frost protection layer), a bituminous sub-base on top of the sand/gravel layer, an asphalt binder layer and an asphalt/concrete layer, more generally known as an asphalt pavement. With respect to a road surface of this type, the invention is concerned with the technical problem of achieving greater durability, in particular with respect to deformation resistance.
This technical problem is firstly and substantially resolved in respect of the road surface in that the bitumen of the asphalt pavement layer and/or of the bituminous sub-base contains a proportion of FT paraffins. The proportion of FT paraffins is preferably in the range from 0.5 to 10%; by weight, further preferably 2.5 to 7.5% by weight. However, volume percentages can also be used here.
Although not always regarded as necessary, it is also within the scope of the invention, as stated, to modify the upper pavement layer, i.e. the asphalt pavement, by addition of FT paraffins. In fact, it has even been found that addition of from 1 to 3% of FT paraffins to the asphalt pavement allows greater strength to be achieved, in particular owing to the greater potential for compaction. More recent knowledge even indicates that the addition of FT paraffins to the asphalt pavement layer is the most important factor with respect to the individual layers of a road surface.
The FT paraffins in this connection are FT paraffins having an SP from 68 to 105xc2x0 C., preferably in chain lengths from C30 to C100 or even C105. The above comments, in particular also with respect to oxidized FT paraffins, apply in the same way here.
The invention is also concerned with a method for the production of a road surface with regard to the technical problem of achieving greater durability.
In this respect, the invention proposes admixing an asphalt mixture for the production of a bituminous sub-base and/or an asphalt binder layer and/or an asphalt pavement in road-building with bitumen containing a proportion from 0.5 to 10%, preferably 2.5 to 7.5%, further preferably 4.5%-5%, suitably in per cent by weight, of FT paraffins. The FT paraffins are preferably added to the liquid bitumen or to the asphalt in solid or liquid form. In respect of a solid form, the FT paraffins here can be, for example, in the form of granules, powder, flakes or pellets. In the flake form, a flake-like substrate is involved. The admixing with the bitumen or asphalt is further preferably carried out at a bitumen temperature from about 160 to 170xc2x0 C. The aggregate, such as stone, gravel or grit, is then added to the bitumen modified in this way.
Overall, it has been found that a bitumen of this type has a higher softening point, with lower penetration. Indeed, the penetration is slightly lower than would have been expected. The softening point rises more quickly than the penetration drops. There was no evidence of separation. The bitumen modified in this way has an advantageously long shelf-life. In addition, the adhesion behavior is improved for approximately the same breaking point compared with conventional bitumen. A corresponding improvement also arises, as also mentioned, in the asphalt mixture produced using this bitumen. Surprisingly, the low-temperature behavior is not impaired. Instead, it is determined by the base bitumen used.
The invention also relates to a method for the production of a road surface containing proportions of used asphalt from a scraped-off road surface and proportions of fresh asphalt, in which the used asphalt is firstly warmed to a temperature which is lower than the temperature of the fresh asphalt, and the proportions of used asphalt and fresh asphalt are then mixed. In a method of this type, the invention proposes the addition of FT paraffin to the fresh asphalt, or if desired to the used asphalt. Surprisingly, this allows better break-up of the used asphalt to be achieved. The used asphalt is only warmed sufficiently that liquefaction does not take place. Instead, the liquefaction and mixing with the fresh asphalt only occur due to the addition of the fresh asphalt and the significantly higher temperature of the fresh asphalt. The fact that FT paraffin is added to the fresh asphalt causes the fresh asphalt to liquefy to a greater extent, resulting in more intimate mixing and thus faster temperature-wise breaking-up of the used asphalt. In this connection, the FT paraffins are preferably added in a proportion from 0.1 to 0.5%, in an example carried out in a proportion of about 0.25%, in each case suitably in per cent by weight based on the amount of fresh asphalt employed.
Road-building bitumen B 100 was prepared with 2.5%, 5% and 7.5% by volume of FT paraffins. The FT paraffins were stirred into the bitumen using a paddle stirrer at 160xc2x0 C. The following values were obtained here:
The following explanations apply to the table:
The softening point was determined using a ring and ball in accordance with Austrian Standard C9212. The penetration was determined in accordance with Austrian Standard C9214. The Fraass breaking point was determined in accordance with Austrian Standard C9213. The thermal stability (tube test) was tested in accordance with TL-Pmb, Part 1 (1991) at +180xc2x0 C. and 72 hours. The adhesive behavior was tested in accordance with Austrian Standard B3682 on the following stones:
EBK 8/11 dolomitic limestone (Bad Deutsch Altenburg); EBK 8/11 dolomite (Gaaden); EBK 8/11 granulite (Meiding); EBK 8/11 granite (Niederschrems).
The xe2x80x9crolling thin film oven testxe2x80x9d heating test was carried out in accordance with ASTM D 2872-88 at 163xc2x0 C., and the weight change, the change in ring-and-ball softening point and the penetration were determined at 25xc2x0 C.
The results show that the addition of FT paraffin results in an increase in the softening point and a reduction in the penetration. The adhesive behavior is improved by addition of FT paraffin in respect of aggregate of various particle size (0-32), such as granite, granulite or dolomitic limestone.
The added FT paraffin was an FT paraffin having the usual chain-length distribution with a maximum of C40 to about C60 obtained from the Fischer-Tropsch synthesis.
A road surface consisting of a pavement layer and an asphalt binder layer was produced. The asphalt layer contained 2-3%xe2x80x94based on the bitumenxe2x80x94of FT paraffins of usual chain length as obtained from the Fischer-Tropsch synthesis.
A significant extension of the possible compaction time of the bituminous sub-base from the 0.5 hour usual hitherto to more than 2 hours was evident owing to improved flow behavior due to the addition of FT paraffins. Processing was still possible at outside temperatures of below 3xc2x0 C. The degree of compaction in the bituminous sub-base and in the pavement layer also increased. For example, degrees of compaction of 97% were usual hitherto. Here, a degree of compaction of more than 100% was achieved. A significant increase in durability with a considerable reduction in the tendency to form wheel tracks was obtained.
Mastic asphalt was prepared with a bitumen content of 7.5. FT paraffins were added to the bitumen in a proportion of 5%, based on the weight of the bitumen. A reduction in the hitherto usual processing temperature (stirring temperature) from 250 to 220xc2x0 C. was obtained. In spite of the reduced processing temperature, the addition of FT paraffins resulted in an improvement in the flow behavior, which resulted in a longer processing life for the mastic asphalt. A significant reduction in the emission values on application of the mastic asphalt was observed owing to the temperature reduction. Overall, more square metres were achieved per time unit during processing since it was possible to process greater amounts of asphalt without having to fear a reduction below the minimum processing temperature necessary.
The track formation on grit mastic asphalt 0/11 S, B 65, was measured. The designation xe2x80x9c0/11xe2x80x9d here represents a stone size of from 0 to 11 mm. The results shown in the following table were achieved. The FT paraffin content is based on the bitumen employed (% by weight).
Comparative experiments were carried out using bitumen B80 and 0% by weight, 1.5% by weight, 3.0% by weight and 4.5% by weight, based on the original binder B80. The results achieved here are shown in the table below.
Further experiments were carried out using B45, B65 and B80, in each case with 4 or 6% of FT paraffin, again in % by weight, based on the starting binder. In addition, corresponding values for a polymer-modified bitumen (PmB45A) and a bitumen B45 containing 30% by weight of Trinidad Epure were determined for comparison. The results are shown in the table below.
Basically, the following general results were obtained here.
FT paraffin can be stirred homogeneously into bitumen at temperatures of 150xc2x0 C. The transition from the solid state to the liquid state, defined by the RandB softening point, is raised very considerably by the added FT paraffin. If the softening points of the starting bitumen are in the range from 50 to 60xc2x0 C., they increase to 85 to 95xc2x0 C. due to the addition of 4% by weight of FT paraffin. By contrast, the penetration only drops slightly. An increase in viscosity in the region of 2 binder grades (B80 to B45) occurs. The behavior at low temperatures changes only very slightly on determination of the Fraass breaking point and shifts by a maximum of 1 binder grade. This thus gives rise to a considerable increase in the plasticity range. It is furthermore evident that the changes are more pronounced, the softer the starting binder selected.